Isothermal Fatigue of 63Sn-37Pb Solder

Abstract

The effects of aging, strain range, hold time at maximum strain and temperature on the isothermal fatigue life of bulk 63Sn-37Pn solder samples over the total strain range (Δ εT ) from 0.3 to 3.0 percent (tension-tension) and within the temperature range of 25° C to 100° C were studied. The cycles to failure (Nf ) were defined as the number of cycles at which the ratio of the maximum tensile stress to the maximum compressive stress starts to drop appreciably. Fatigue life increases rapidly after a day or two of aging after heat treatment at 150° C for 2 hours followed by air cooling but levels off after a week. The log of fatigue life decreases linearly with increasing log of plastic strain range above Δ εT = 0.6 percent. Hold time at maximum strain dramatically decreases the cycles to failure, however, an increase of hold time more than a few minutes eventually leads to a constant Nf . Temperature variation from 25°C to 100° C was found to have little effect on the fatigue life of the solder in tests with and without hold time. Separation of Pb-rich and Sn-rich phases and cracking of the Sn-rich phases are the main modes of fracture under all conditions used. Damage is concentrated along crisscrossing shear bands oriented approximately 45 deg to the load direction.